The present invention relates to combustors for gas turbines. More specifically, the present invention relates to the portion of the gas turbine combustor that forms the coupling for connecting the combustor to a cross-flame tube.
A gas turbine combustor is typically comprised of a plurality of approximately cylindrical combustors circumferentially arranged within a combustor shell and surrounding the turbine rotor. The combustors are connected by cross-flame tubes. In addition, two adjacent ones of the combustors have high energy electric igniters. At start-up, ignition is established in the fuel/air mixtures in the combustors having igniters, thereby creating a flame. The cross-flame tubes then carry this flame from combustor to combustor around the array until a flame has been established in all of the combustors. Flame detectors in the two combustors that are opposite those with igniters verify that a flame has been established in each of the combustors. During operation, the cross-flame tubes act to re-establish combustion in any combustor that may experience a flame-out.
Traditionally, the cross-flame tubes were formed from a flexible metal hose having flanges at each end. The cross-flame tubes were attached to the combustors by ring-type compression clamps, commonly referred to as "marmon" clamps, that mated with couplings that projected from the combustors. Each coupling was formed by a substantially radially extending tube that was attached to the combustor at the proximal end of the tube and that had a flange formed on its distal end.
Typically, combustors are formed from a plurality of concentric rings joined by corrugations. These rings are cooled by flowing cooling air along the inner walls of the rings, thereby providing a thermal barrier against the heat emanating from the combustion zone within the combustor. This cooling air is introduced by annular cooling air passages formed between adjacent rings that allow the cooling air to enter the combustor and flow over the inner wall of the downstream ring.
Unfortunately, the presence of the cross-flame tube coupling disrupts the flow of cooling air along the inner wall of the ring. As a result, this cooling air scheme has proven ineffective in the portion of the ring downstream of the cross-flame tube coupling and at the inlet to the coupling tube. One solution attempted in the past involved supplying additional cooling air in the vicinity of the coupling by drilling a number of small holes around the circumference of the coupling adjacent the ring or in the ring itself in the portion that surrounds the coupling. However, this approach has not proven entirely successful.
It is therefore desirable to provide a gas turbine combustor having a cross-flame tube coupling in which a flow of cooling air is directed to the end of the coupling tube and over the combustor wall adjacent the coupling.